Because of the absence of unsaturated bonds in the main chain, ethylene·α-olefin copolymers and ethylene·α-olefin·non-conjugated diene copolymers outperform diene rubbers in terms of weather resistance, heat resistance and ozone resistance and are therefore widely used in products such as automobile industrial parts, industrial rubber products, electrical insulating materials, civil engineering and building articles, and rubber products including rubber-coated fabrics.
In particular, ethylene·α-olefin·non-conjugated polyene copolymers have found a wide use because of the fact that the double bonds derived from the non-conjugated polyenes can participate in crosslinking reactions and the copolymers, by undergoing the crosslinking reactions, can achieve a further increase in strength and rubber elasticity of rubber products.
The production of rubber products using ethylene·α-olefin·non-conjugated diene copolymers usually involves the addition of large amounts of inorganic fillers such as carbon blacks, calcium carbonate and talcs and plasticizers such as process oils.
However, the addition of large amounts of inorganic fillers such as carbon blacks, calcium carbonate and talcs and plasticizers such as process oils results in a marked decrease in shaping processability such as rolling processability and extrusion processability as well as in a marked deterioration in mechanical characteristics and rubber elasticity of rubber products obtained by crosslinking.
For example, one approach which has been proposed in order to obtain ethylene·α-olefin·non-conjugated diene copolymers with excellent fillability is to use an ethylene·α-olefin·non-conjugated diene copolymer which has an intrinsic viscosity [η] measured at 135° C. in decalin solvent of 3.7 to 4.1 dl/g (Patent Literature 1: JP-A-H06-1893), or to use an ethylene·α-olefin·non-conjugated diene copolymer having high molecular weight such as a copolymer (A) which includes ethylene, an α-olefin of 6 to 12 carbon atoms and a cyclic non-conjugated diene and has a polystyrene equivalent mass average molecular weight (Mw) in the range of 450,000 to 3,000,000 or a copolymer (B) which includes ethylene, propylene, an α-olefin of 6 to 12 carbon atoms and a cyclic non-conjugated diene and has a similar molecular weight (Patent Literature 2: JP-A-H09-151283).
However, even the use of the ethylene·α-olefin·non-conjugated diene copolymer disclosed in Patent Literature 1 or Patent Literature 2 (with an intrinsic viscosity [η] of about 4 dl/g) does not allow the desired rubber elasticity to be exhibited without crosslinking and thus it is difficult for such a copolymer to be used in applications where the copolymer is filled with significantly large amounts of additives.
Although Patent Literature 2 does not disclose any intrinsic viscosity [η] values, EP98A, product name, manufactured by JSR Corporation that is described in Comparative Example 3 [an ethylene/propylene/5-ethylidene-2-norbornene random copolymer having ethylene content: 75.9 mol %, propylene content: 22.6 mol %, ENB content: 1.16 mol %, Mw 1,179,000 and Mw/Mn 4.4, and containing 75 parts by mass of a paraffin process oil as an extender oil] was obtained and the intrinsic viscosity [η] of the random copolymer was measured after the removal of the extender oil, the measurement resulting in 4.45 dl/g.
In one shaping method, a film or sheet having a constant thickness is continuously formed by rolling a thermoplastic polymer through two or more rolls (a calendering method).
The calendering method achieves a higher output than by a usual extrusion method and thus allows films or sheets to be produced at low cost. Conventionally, the calendering method most often involves polyvinyl chloride containing various plasticizers, and is used in mass production of articles such as leathers, sheets and films. In recent years, due to the VOC problem associated with polyvinyl chloride and also because the incineration of wastes causes problematic generation of gas, there has been a demand that the material be replaced by alternatives.
Materials including olefin polymers have been regarded as promising alternatives to polyvinyl chloride. However, highly crystalline materials such as high-density polyethylenes and polypropylenes have problems in flexibility and also exhibit a drastic change in viscosity when being molten. Thus, these materials have problems such as that the suitable range in which calendering is feasible is limited, that the materials exhibit poor releasability from the calender rolls, and that the calendered products have low surface smoothness and tend to be nonuniform in thickness.
On the other hand, α-olefin copolymers, which are low crystalline olefin materials, have very low calendering properties due to such problems as poor release and engagement failure. The term poor release means that the resin is not separated from the rolls and becomes twisted around the rolls. The term engagement failure means that the resin is not engaged between the rolls and the bank continues to increase its size. These problems tend to be worsened when the materials are formulated to become more flexible by the addition of plasticizers such as oils.
Many solutions to the above problems have been proposed. For example, Patent Literature 3 discloses a blend suited for calendering which includes a broad molecular weight distribution polypropylene. Patent Literature 4 discloses a calendering method which involves a composition including a propylene/ethylene random copolymer and a propylene/ethylene block copolymer. Patent Literature 5 proposes a soft syndiotactic polypropylene composition based on a syndiotactic propylene polymer and including a syndiotactic structure propylene·ethylene copolymer, an amorphous α-olefin copolymer, an ethylene·α-olefin copolymer and an isotactic propylene polymer.
In order to improve the releasability from calender rolls, Patent Literature 6 discloses a composition including a polypropylene resin composition and an aliphatic monocarboxylic acid metal salt. However, no films with sufficient performance have been obtained.